This invention pertains to methods for environmentally acceptable treatment and disposal of incinerator ashes, particularly incinerator fly ashes containing heavy metal and soluble constituents.
Waste incinerators, resource recovery units (RRUs) and certain other types of combustion equipment often produce, as by-products, various types of ash products. The most common of these is bottom ash, which comprises the solid remains of the material incinerated, and fly ash. Fly ash is typically a finely divided ash by-product which escapes with stack gases and is captured by various types of pollution control devices such as a baghouse or an electrostatic precipitator. As the number of ash-producing plants and the amount of ash produced have increased, disposal of this ash has become an increasing problem. Recycling will help reduce the ash problem to a certain extent, but with landfill space at a premium in many states, more RRUs are planned. Thus the ash problem may continue to grow.
An environmentally acceptable method for disposing of these ash by-products is badly needed. This is particularly true as to those ash products, typically fly ashes, which have a significant soluble fraction and heavy metal constituents. The soluble constituents may cause ground water pollution problems. The heavy metals, which are usually also in the soluble fraction, are also considered dangerous ground water pollutants. Many of these heavy metals are toxic or are present in the ash in toxic proportions.
The toxic metals of greatest concern are cadmium and lead, but other metals, such as zinc may become a problem as the metal concentration in the incinerator ash increases. The ash cannot simply be disposed of in a landfill because these concentrations of heavy metals tend to leach and contaminate the surrounding soil or ground water.
Processes have been proposed to fixate or encapsulate the ash, but none have adequately dealt with the high concentration of heavy metals present in waste incinerator ash.